1. Field of the Invention
The present invention generally relates to production of microfabricated devices and, in particular, to a system and method for reducing contamination within a microfabricated device by preventing bonding material from dissolving with layers within the device.
2. Related Art
Some conventional microfabricated devices, such as semiconductor laser assemblies, include a compliant layer that can move or deform to absorb mechanical strain. In this regard, different layers of a typical microfabricated device usually have different thermal expansion properties and, therefore, expand/contract differently when exposed to temperature variations. The difference in thermal expansion and/or contraction creates mechanical strain within the microfabricated device. The compliant layer is usually comprised of a soft material, such as gold (Au), so that it can deform to absorb the mechanical strain. U.S. Pat. No. 5,559,817 entitled xe2x80x9cCompliant Layer Metallization,xe2x80x9d and filed by Derkits, Jr., et al. on Nov. 23, 1994, which is incorporated herein by reference, fully discusses utilization of a compliant metallization layer to absorb mechanical strain within microfabricated devices.
Since one of the primary purposes of the compliant layer is to absorb mechanical strain, it is important to ensure that the mechanical properties of the compliant layer remain unaltered by protecting the chemical integrity of the compliant layer. However, it is possible for the compliant layer to become contaminated when components are bonded to the microfabricated device. In this regard, it is possible for a bonding material, such as a solder, to react with (i.e., contaminate) the elements of the compliant layer, if the bonding material is allowed to contact the compliant layer. Contamination of the compliant layer can harden the compliant layer, thereby making it more difficult for the compliant layer to absorb mechanical strain. Consequently, it is common to couple a thick barrier layer to the compliant layer. The thick barrier layer separates the compliant layer from the bonding material in order to protect the chemical integrity of the compliant layer.
Furthermore, in many applications it is also important to maintain the thermal and/or electrical conductivity of the compliant layer and/or other layers in the microfabricated device. However, reaction with the bonding material can adversely affect the thermal and/or electrical conductivity of the layers of the device. Therefore, by preventing the bonding material from reacting with the layers underlying the barrier layer, the barrier layer is also used to protect the thermal and/or electrical conductivity of the device.
However, many conventional barrier layers begin to dissolve during long (or sequential) annealing processes and/or at relatively high temperatures, thereby allowing the bonding material to react with and contaminate the compliant layer and/or other layers underlying the barrier layer. Therefore, the chemical integrity and/or the transport properties (i.e., the thermal and/or electrical conductivity) of the layer(s) beneath the barrier layer are adversely affected.
Another problem that occurs when the barrier layer is dissolved by the bonding material is contamination of the bonding material. In this regard, the melting temperature of the bonding material is usually affected as the material of the barrier layer and/or layers residing underneath the barrier layer are dissolved into the bonding material. As a result, the bonding material may solidify before a bond is fully formed thereby reducing the quality of the bond.
Thus, a heretofore unaddressed need exists in the industry for a more robust barrier layer that resists dissolving with bonding material to protect the chemical integrity of the bonding material and to protect the chemical integrity and/or the transport properties of underlying layers during bonding at relatively high temperatures and/or for relatively long or sequential bonding periods.
The present invention overcomes the inadequacies and deficiencies of the prior art as discussed herein. The present invention is a system and method for preventing bonding material from contaminating layers within a microfabricated device.
The present invention utilizes a barrier layer to separate bonding material from an underlying layer that is located beneath the barrier layer. The barrier layer includes at least three thin layers that have alternating levels of electronegativity. Therefore, a significant amount of intermetallics are formed between the thin layers, thereby creating strong bonds between the thin layers at relatively low temperatures. It is difficult for the bonding material to break the strong bonds of the thin layers, and the bonding material is, therefore, prevented from penetrating the barrier layer and reacting with the underlying layer.
The present invention can also be viewed as providing a method for manu-facturing a microfabricated device. Briefly described, the method can be broadly conceptualized by the following steps: providing a substrate; forming a barrier layer; and forming an underlying layer between the substrate and the barrier layer. The forming of a barrier layer step includes the steps of: forming a first layer on a second layer; forming a third layer on the second layer; and selecting a respective thickness for each of the first, second, and third layers such that intermetallics form throughout the first, second, and third layers.
The present invention has many advantages, a few of which are delineated hereafter, as mere examples.
An advantage of the present invention is that bonding material is prevented from contacting and reacting with layers of a microfabricated device that are located beneath a barrier layer. Therefore, the bonding material is prevented from contaminating the layers located beneath the barrier layer.
Another advantage of the present invention is that evaporation techniques may be used to form a barrier layer within a microfabricated device.
Another advantage of the present invention is that intermetallics may be formed throughout a barrier layer within a microfabricated device.
Another advantage of the present invention is that high temperatures and/or long (or sequential) bonding process may be applied to a microfabricated device without contaminating the material of the device.
Another advantage of the present invention is that contamination of bonding material used to bond components of a microfabricated device can be reduced or prevented.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following detailed description, when read in conjunction with the accompanying drawings. It is intended that all such features and advantages be included herein within the scope of the present invention, as is defined by the claims.